Aircraft structures are increasingly being constructed from new materials. It is desirable, and often required, that significant testing be performed on the new materials prior to their being incorporated into an aircraft structure. Once the material has been determined suitable for use in an aircraft, each lot of material must be tested at various stages of the production to ensure that the material is properly constructed. The testing includes the testing of incoming material from a third party prior to constructing the material for use in the aircraft. The testing may also include testing the material after final construction, just prior to incorporation into an aircraft structure. This invention is related to U.S. patent application Ser. No. 173,485, filed Mar. 25, 1988 by Reid et al. which describes other methods and apparatuses for preparing specimens.
One of the types of material recently in use in an aircraft structure is a composite material. Composite materials include various resins, fibers and graphite epoxy composites of various compositions. One method of testing the graphite epoxy composite material is load test samples of the material. To load test samples, test specimens are produced from the sheets of material which will be used in the aircraft structure. The specimens are subjected to destructive load tests to determine the loads which the material will carry prior to failure. The destructive load tests include tensile tests, in which the specimen is placed in tension and the load increased until the member fails, and a compression test, in which the test specimen is placed in compression and the load increased until the specimen fails. Ideally, the amount of load held by the specimen until failure is an indication of the quality of the material. If all of the specimens from a lot fail under a very small load, the lot of material is likely defective. If the lot of material is found defective, it will be rejected for use on the aircraft.
One problem in the prior art is the difficulty of producing specimens which accurately reflect the quality of the lot of material. In the prior art, the specimens are prepared from the larger sheet taken from the lot. The specimens are cut from the sheet and tested in the laboratory. Frequently, using prior art techniques of specimen testing, the load carried by the specimens within the single sheet were significantly different. Some specimens fail under very small loads, while other specimens from the very same sheet carry large loads prior to failure. When the failure point of specimens within the same lot is not uniform, the quality of the lot is difficult to determine and often requires additional specimens, with further testing to be performed. A further problem in the prior art is that significant time is required to prepare the specimens using prior art techniques. Additional time is required to prepare the large number of specimens for testing until a sufficiently uniform test result is achieved to provide an indication of the quality of the material being tested.